U.S. patent application number 12/066708 was filed with the patent office on 2010-04-01 for position tracking method, position tracking device, and ultrasonograph.
Invention is credited to Takao SUZUKI.
Application Number | 20100081929 12/066708 |
Document ID | / |
Family ID | 37864921 |
Filed Date | 2010-04-01 |
United States Patent
Application |
20100081929 |
Kind Code |
A1 |
SUZUKI; Takao |
April 1, 2010 |
POSITION TRACKING METHOD, POSITION TRACKING DEVICE, AND
ULTRASONOGRAPH
Abstract
The location tracking method of the present invention is a
method for tracking the motion of a measuring point on an object by
repeatedly irradiating the object with waves and analyzing received
signals that are based on the waves reflected from the object, and
includes the steps of: (A) irradiating the object with a wave and
calculating an initial phase curve showing a phase shift of a
received signal in a wave propagation direction with respect to a
reference signal, the received signal being based on the wave
reflected; (B) setting an initial location in the propagating
direction and assigning the measuring point to the initial
location; (C) defining a displacement line, which passes the
initial location on the initial phase curve and of which the
gradient is calculated based on the frequency of the reference
signal; and (D) irradiating the object with the waves multiple
times, thereby calculating phase curves, each representing a phase
shift of the received signal with respect to the reference signal,
and defining the intersection between the displacement line and
each phase curve as a location to which the measuring point has
been displaced.
Inventors: |
SUZUKI; Takao; (Kanagawa,
JP) |
Correspondence
Address: |
MARK D. SARALINO (PAN);RENNER, OTTO, BOISSELLE & SKLAR, LLP
1621 EUCLID AVENUE, 19TH FLOOR
CLEVELAND
OH
44115
US
|
Family ID: |
37864921 |
Appl. No.: |
12/066708 |
Filed: |
September 12, 2006 |
PCT Filed: |
September 12, 2006 |
PCT NO: |
PCT/JP2006/318021 |
371 Date: |
March 13, 2008 |
Current U.S.
Class: |
600/437 ;
367/99 |
Current CPC
Class: |
A61B 8/08 20130101; A61B
8/485 20130101; G01S 7/52042 20130101; G01S 7/52025 20130101; G01S
7/52071 20130101; A61B 8/04 20130101; G01S 15/66 20130101; G01S
7/52087 20130101 |
Class at
Publication: |
600/437 ;
367/99 |
International
Class: |
A61B 8/04 20060101
A61B008/04; G01S 15/06 20060101 G01S015/06 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 14, 2005 |
JP |
2005-266785 |
Claims
1. A location tracking method for tracking the motion of a
measuring point that has been set on an object of measurement by
repeatedly irradiating the object with waves and by analyzing
received signals that are based on the waves reflected from the
object, the method comprising the steps of: (A) irradiating the
object with a wave and calculating an initial phase curve showing a
phase shift of a received signal in a propagation direction of the
wave with respect to a reference signal, the received signal being
based on the wave reflected; (B) setting an initial location in the
wave propagating direction and assigning the measuring point to the
initial location; (C) defining a displacement line, which passes
the initial location on the initial phase curve and of which the
gradient is calculated based on the frequency of the reference
signal; and (D) irradiating the object with the waves a number of
times, thereby calculating phase curves, each representing a phase
shift of the received signal with respect to the reference signal,
and defining the intersection between the displacement line and
each said phase curve as a location to which the measuring point
has been displaced.
2. The location tracking method of claim 1, wherein the received
signal is discrete quantized digital data, and wherein the step (D)
includes calculating the newest phase curve by figuring out a phase
difference between the newest received signal and the signal that
has been received the previous time and by adding the phase
difference thus obtained to the previous phase curve.
3. The location tracking method of claim 1, wherein the received
signal is discrete quantized digital data, and wherein the step (D)
includes calculating the newest phase curve by figuring out a phase
difference between the newest received signal and the signal that
has been received the previous time at one of multiple sample
points that have been set in the wave propagating direction, adding
the phase difference thus obtained to a phase at the one sample
point on the previous phase curve, and sequentially adding the
phase difference of the newest received signal in a depth direction
to the sum.
4. The location tracking method of claim 1, wherein the received
signal is discrete quantized digital data, and wherein the step (C)
includes determining a phase at the initial location by subjecting
sampled data values of multiple phases to interpolation.
5. The location tracking method of claim 1, wherein the received
signal is discrete quantized digital data, and wherein the step (D)
includes finding an intersection either between multiple
approximation lines, obtained based on sampled data of multiple
phases, or between an approximation curve and the displacement
line.
6. A location tracking method for tracking the motion of a
measuring point that has been set on an object of measurement by
repeatedly irradiating the object with waves and by analyzing
received signals that are based on the waves reflected from the
object, the method comprising the steps of: (A) irradiating the
object with a wave to obtain a first received signal that is based
on the wave reflected; (B) calculating a first phase curve showing
a phase shift of the first received signal in a propagation
direction of the wave with respect to a reference signal; (C)
setting a first location in the wave propagating direction and
assigning the measuring point to the first location; (D) defining a
displacement line, which passes the first location on the first
phase curve and of which the gradient is calculated based on the
frequency of the reference signal; (E) irradiating the object with
a wave, thereby calculating a second phase curve, representing a
phase shift of the second received signal with respect to the
reference signal; and (F) defining the intersection between the
displacement line and the second phase curve as a second location
to which the measuring point has been displaced, wherein the
location of the measuring point is tracked by performing the steps
(B) through (E) all over again with the second received signal of
the step (E) and the second location of the step (F) substituted
for the first received signal and the first location,
respectively.
7. The location tracking method of claim 6, wherein the step (E)
includes calculating the second phase curve by figuring out a phase
difference between the first and second received signals and by
adding the phase difference thus obtained to the first phase
curve.
8. The location tracking method of claim 6, wherein the step (E)
includes calculating the second phase curve by figuring out a phase
difference between the first and second received signals at one of
multiple sample points that have been set in the wave propagating
direction, adding the phase difference thus obtained to a phase at
the one sample point on the first phase curve, and sequentially
adding the phase difference of the second received signal in a
depth direction to the sum.
9. The location tracking method of claim 8, wherein the step (E)
includes setting one of the sample points closest to the measuring
point.
10. The location tracking method of claim 9, wherein the step (E)
includes calculating a portion of the second phase curve according
to the sign of the phase difference between the first and second
received signals and defining the intersection between the
displacement line and that portion of the second phase curve as the
location to which the measuring point has been displaced.
11. The location tracking method of claim 6, wherein the step (B)
includes calculating the first phase curve based on only the first
received signal.
12. The location tracking method of claim 6, wherein the step (B)
includes calculating a portion of the first phase curve by finding
phases at multiple sample points that have been set in the wave
propagating direction.
13. A location tracking method for tracking the motion of a
measuring point that has been set on an object of measurement by
repeatedly irradiating the object with waves and by analyzing
received signals that are based on the waves reflected from the
object, the method comprising the steps of: (A) irradiating the
object with a wave to obtain a first received signal that is based
on the wave reflected; (B) calculating a first phase curve showing
a phase shift of the first received signal in a propagation
direction of the wave with respect to a reference signal; (C)
setting a first location in the wave propagating direction and
assigning the measuring point to the first location; (D) defining a
displacement line, which passes one of multiple sample points that
have been set in the wave propagating direction and of which the
gradient is calculated based on the frequency of the reference
signal, the one sample point being located closest to the first
location; (E) irradiating the object with a wave, thereby
calculating a second phase curve representing a phase shift of the
second received signal with respect to the reference signal; and
(F) finding the intersection between the displacement line and the
second phase curve, adding the distance from the intersection to
the sample point that is closest to the first location to the
location of the measuring point to set a second location, and
defining the second location as a location to which the measuring
point has been displaced, wherein the location of the measuring
point is tracked by performing the steps (B) through (F) all over
again with the second received signal of the step (E) and the
second location of the step (F) substituted for the first received
signal and the first location, respectively.
14. The location tracking method of claim 13, wherein the step (E)
includes the steps of: (E1) calculating the phase difference
between the first and second received signals at the sample point
that is located closest to the first location; (E2) adding the
phase difference, calculated in the step (E1), to the phase at the
closest sample point on the first phase curve, thereby calculating
the phase of the second received signal at that closest sample
point; (E3) calculating phase differences for multiple sample
points that are adjacent to the closest sample point; and (E4)
defining either an approximation line or an approximation curve as
the second phase curve based on the phase that has been calculated
in the step (E2) and the phase difference that has been calculated
in the step (E3).
15. The location tracking method of claim 1, wherein if the unit of
the distance axis of a distance-phase plane is a length unit, the
gradient of the displacement line is calculated -4.pi.f/C, where f
is the frequency of the reference signal and C is the propagation
velocity of the waves.
16. The location tracking method of claim 1, wherein if the unit of
the distance axis of a distance-phase plane is a receiving time
unit, the gradient of the displacement line is calculated -2.pi.f,
where f is the frequency of the reference signal.
17. An apparatus for tracking the location of an object of
measurement, the apparatus comprising: a transmitting section for
irradiating the object with a wave; a receiving section for
receiving a wave that has been reflected from the object to
generate a received signal; and a tracking section for tracking the
location of a measuring point that has been set on the object by
the method of claim 1 in cooperation with the transmitting and
receiving sections.
18. An ultrasonic diagnostic apparatus comprising: a transmitting
section for transmitting an ultrasonic wave toward an object of
measurement using a probe; a receiving section for receiving a wave
that has been reflected from the object through the probe to
generate a received signal; and a tracking section for tracking the
location of a measuring point that has been set on the object by
the method of claim 1 in cooperation with the transmitting and
receiving sections, wherein the apparatus evaluates at least one of
the shape property and the attribute property of the object based
on the location of the measuring point that has been calculated by
the tracking section.
19. The ultrasonic diagnostic apparatus of claim 18, wherein the
attribute property is one of the magnitude of strain, elasticity
and viscosity of the object.
20. The ultrasonic diagnostic apparatus of claim 18, further
comprising an elasticity calculating section that receives a signal
representing a variation in stress applied to the object and that
calculates the elasticity of the object based on the location of
the measuring point that has been detected by the tracking
section.
21. The ultrasonic diagnostic apparatus of claim 20, wherein the
object of measurement is a vascular wall and the signal
representing the variation in stress is a blood pressure
waveform.
22. The ultrasonic diagnostic apparatus of claim 18, wherein the
object of measurement is a vascular wall and the attribute property
is a diagnostic index of arterial sclerosis including at least one
of an intima-media thickness (IMT) and a pulse wave velocity
(PWV).
23. The ultrasonic diagnostic apparatus of claim 18, wherein the
object of measurement is a heart and the shape property is a
contraction/dilation property.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method and apparatus for
tracking the location of an object of measurement by repeatedly
irradiating the object with waves and detecting the waves reflected
from the object, and also relates to an ultrasonic diagnostic
apparatus.
BACKGROUND ART
[0002] An ultrasonic diagnostic apparatus is used to make a
noninvasive checkup on a subject by irradiating him or her with an
ultrasonic wave and analyzing the information contained in its echo
signal. For example, a conventional ultrasonic diagnostic apparatus
that has been used extensively converts the intensity of an echo
signal into its associated pixel luminance, thereby presenting the
subject's structure as a tomographic image. In this manner, the
internal structure of the subject can be known.
[0003] Meanwhile, some people are attempting recently to track the
motion of a subject's tissue more precisely and evaluate the strain
and the elasticity, viscosity or any other physical (attribute)
property of the tissue mainly by analyzing the phase of the echo
signal.
[0004] Patent Document No. 1 discloses a method for tracking a
subject's tissue highly precisely by calculating the magnitude of
instantaneous displacement of a local region of the subject based
on the phase difference of an ultrasonic echo signal to be
transmitted and received at regular intervals and by summing the
magnitudes of displacements together. Hereinafter, a method for
tracking a subject's tissue as disclosed in Patent Document No. 1
will be described with reference to FIG. 1. Suppose ultrasonic
pulses are transmitted toward the same location of a subject at
regular intervals .DELTA.T and received signals, generated by
converting the resultant echo signals into electrical signals, are
identified by y1(t) and y2(t), respectively, where t represents the
receiving time when the transmitting time is zero. The distance x
from the probe (which will be simply referred to herein as a
"distance") and the receiving time t, which is the amount of time
it takes for the received signal to arrive since its transmitting
time, satisfy the following Equation (1), provided that C is the
sonic velocity.
t1=x/(C/2) (1)
[0005] The received signals y1(t) and y2(t), which are functions of
time, can be converted into y1(x) and y2(x) that are functions of
distance by using Equation (1). Suppose there is a measuring point
at a distance X and the measuring point has displaced .DELTA.X
parallel to the propagation direction of an ultrasonic wave during
an interval .DELTA.T. According to Patent Document No. 1, to
calculate the magnitude of this displacement .DELTA.X of the
measuring point during the interval .DELTA.T, orthogonal detection
is carried out on y1(X) and y2(X) using a reference signal that has
a frequency f. If the phase difference obtained by the orthogonal
detection is .DELTA..theta., the following Equation (2) is
satisfied.
.DELTA.X=-C.DELTA..theta./4.pi.f (2)
[0006] The location X' of the measuring point after the interval
.DELTA.T has passed is given by adding the magnitude of
displacement .DELTA.X, given by Equation (2), to the original
measuring point X as in the following Equation (3).
X'=X+.DELTA.X (3)
[0007] By performing this calculation repeatedly, the location of
the measuring point in the subject can be tracked. For example, if
the received signal that has been transmitted and received next is
y3(x), the location X'' of the measuring point in 2.DELTA.T can be
calculated by substituting the phase difference .DELTA..theta.'
between y2(X') and y3(X') into Equation (2) and then substituting
the resultant .DELTA.X' into Equation (3).
[0008] Patent Document No. 2 further develops the method of Patent
Document No. 1 into a method of calculating the elasticity of a
subject's tissue (e.g., an arterial vascular wall, in particular).
According to this method, first, an ultrasonic wave is transmitted
from a probe 101 toward the vascular wall 302 of a subject 304 as
shown in FIG. 2(a). And the echo signals, reflected from measuring
points A and B on the vascular wall 302, are analyzed by the method
of Patent Document No. 1, thereby tracking the motions of the
measuring points A and B. FIG. 2(b) shows the tracking waveforms TA
and TB of the measuring points A and B along with an
electrocardiographic complex ECG.
[0009] As shown in FIG. 2(b), the tracking waveforms TA and TB have
the same periodicity as the electrocardiographic complex ECG, which
shows that the artery dilates and shrinks in sync with the cardiac
cycle of the heart. More specifically, when the
electrocardiographic complex ECG has outstanding peaks called "R
waves", the heart starts to shrink, thus pouring blood flow into
the artery and raising the blood pressure. As a result, the
vascular wall is dilated rapidly. That is why soon after the R wave
has appeared on the electrocardiographic complex ECG, the artery
dilates rapidly and the tracking waveforms TA and TB rise steeply,
too. After that, however, as the heart dilates slowly, the artery
shrinks gently and the tracking waveforms TA and TB gradually fall
to their original levels. The artery repeats such a motion
cyclically.
[0010] The difference between the tracking waveforms TA and TB is
represented as a waveform W showing a variation in thickness
between the measuring points A and B. Supposing the maximum
variation of the thickness variation waveform is .DELTA.W and the
reference thickness between the measuring points A and B during
initialization (i.e., the end of the diastole) is Ws, the magnitude
of maximum strain .epsilon. between the measuring points A and B is
calculated by the following Equation (4).
.epsilon.=.DELTA.W/Ws (4)
[0011] As this strain is caused due to the difference between the
blood pressures applied to the vascular wall, the elasticity Er
between the measuring points A and B is given by the following
Equation (5), provided that .DELTA.P is the blood pressure
difference at this time.
Er=.DELTA.P/.epsilon.=.DELTA.PWs/.DELTA.W (5)
[0012] Therefore, by measuring the elasticity Er for multiple spots
on a tomographic image, an image representing the distribution of
elasticities can be obtained. If an atheroma 303 has been created
in the vascular wall 302 as shown in FIG. 2(a), the atheroma 303
and its surrounding vascular wall tissue have different
elasticities. That is why if an image representing the distribution
of elasticities is obtained, important information can be acquired
in inspecting the attribute of the atheroma (e.g., how easily the
atheroma may rupture, among other things).
[0013] Likewise, the viscosity .mu. disclosed in Non-Patent
Document No. 1 can also be calculated by this measuring method. The
viscosity .mu., which is an important index representing an
attribute of the vascular wall tissue, is given by the following
equation.
P=.mu.d.epsilon./dt+E.epsilon. [0014] Patent Document No. 1:
Japanese Patent Application Laid-Open Publication No. 10-5226
[0015] Patent Document No. 2: Japanese Patent Application Laid-Open
Publication No. 2000-229078 [0016] Non-Patent Document No. 1:
Hiroshi Kanai, edited by the Acoustical Society of Japan, "Spectral
Analysis of Sounds and Vibrations", Corona Publishing Co., Ltd.,
ISBN4-339-01105-3
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
[0017] According to the method disclosed in Patent Document No. 1,
however, if echoes that have been received from multiple sources of
reflection are superposed one upon the other, then the received
signals have disturbed phases, thus making it impossible to track
the measuring point accurately. Among other things, since a vital
tissue scatters a wave received, sometimes the tracking cannot be
done accurately and a tissue attribute such as the elasticity
cannot be measured precisely for that reason.
[0018] An object of the present invention is to provide a method
and apparatus for tracking the location of a measuring point
accurately even in such a situation where echoes from multiple
sources of reflection are superposed one upon the other and where
the received signals have disturbed phases, and also provide an
ultrasonic diagnostic apparatus that adopts such a method and
apparatus.
Means for Solving the Problems
[0019] A location tracking method according to the present
invention is a method for tracking the motion of a measuring point
that has been set on an object of measurement by repeatedly
irradiating the object with waves and by analyzing received signals
that are based on the waves reflected from the object. The method
includes the steps of: (A) irradiating the object with a wave and
calculating an initial phase curve showing a phase shift of a
received signal in a propagation direction of the wave with respect
to a reference signal, the received signal being based on the wave
reflected; (B) setting an initial location in the wave propagating
direction and assigning the measuring point to the initial
location; (C) defining a displacement line, which passes the
initial location on the initial phase curve and of which the
gradient is calculated based on the frequency of the reference
signal; and (D) irradiating the object with the waves a number of
times, thereby calculating phase curves, each representing a phase
shift of the received signal with respect to the reference signal,
and defining the intersection between the displacement line and
each said phase curve as a location to which the measuring point
has been displaced.
[0020] In one preferred embodiment, the received signal is discrete
quantized digital data, and the step (D) includes calculating the
newest phase curve by figuring out a phase difference between the
newest received signal and the signal that has been received the
previous time and by adding the phase difference thus obtained to
the previous phase curve.
[0021] In another preferred embodiment, the received signal is
discrete quantized digital data, and the step (D) includes
calculating the newest phase curve by figuring out a phase
difference between the newest received signal and the signal that
has been received the previous time at one of multiple sample
points that have been set in the wave propagating direction, adding
the phase difference thus obtained to a phase at the one sample
point on the previous phase curve, and sequentially adding the
phase difference of the newest received signal in a depth direction
to the sum.
[0022] In still another preferred embodiment, the received signal
is discrete quantized digital data, and the step (C) includes
determining a phase at the initial location by subjecting sampled
data values of multiple phases to interpolation.
[0023] In yet another preferred embodiment, the received signal is
discrete quantized digital data, and the step (D) includes finding
an intersection either between multiple approximation lines,
obtained based on sampled data of multiple phases, or between an
approximation curve and the displacement line.
[0024] Another location tracking method according to the present
invention is a method for tracking the motion of a measuring point
that has been set on an object of measurement by repeatedly
irradiating the object with waves and by analyzing received signals
that are based on the waves reflected from the object. The method
includes the steps of: (A) irradiating the object with a wave to
obtain a first received signal that is based on the wave reflected;
(B) calculating a first phase curve showing a phase shift of the
first received signal in a propagation direction of the wave with
respect to a reference signal; (C) setting a first location in the
wave propagating direction and assigning the measuring point to the
first location; (D) defining a displacement line, which passes the
first location on the first phase curve and of which the gradient
is calculated based on the frequency of the reference signal; (E)
irradiating the object with a wave, thereby calculating a second
phase curve, representing a phase shift of the second received
signal with respect to the reference signal; and (F) defining the
intersection between the displacement line and the second phase
curve as a second location to which the measuring point has been
displaced. The location of the measuring point is tracked by
performing the steps (B) through (E) all over again with the second
received signal of the step (E) and the second location of the step
(F) substituted for the first received signal and the first
location, respectively.
[0025] In one preferred embodiment, the step (E) includes
calculating the second phase curve by figuring out a phase
difference between the first and second received signals and by
adding the phase difference thus obtained to the first phase
curve.
[0026] In another preferred embodiment, the step (E) includes
calculating the second phase curve by figuring out a phase
difference between the first and second received signals at one of
multiple sample points that have been set in the wave propagating
direction, adding the phase difference thus obtained to a phase at
the one sample point on the first phase curve, and sequentially
adding the phase difference of the second received signal in a
depth direction to the sum.
[0027] In this particular preferred embodiment, the step (E)
includes setting one of the sample points closest to the measuring
point.
[0028] In a specific preferred embodiment, the step (E) includes
calculating a portion of the second phase curve according to the
sign of the phase difference between the first and second received
signals and defining the intersection between the displacement line
and that portion of the second phase curve as the location to which
the measuring point has been displaced.
[0029] In still another preferred embodiment, the step (B) includes
calculating the first phase curve based on only the first received
signal.
[0030] In yet another preferred embodiment, the step (B) includes
calculating a portion of the first phase curve by finding phases at
multiple sample points that have been set in the wave propagating
direction.
[0031] Still another location tracking method according to the
present invention is a method for tracking the motion of a
measuring point that has been set on an object of measurement by
repeatedly irradiating the object with waves and by analyzing
received signals that are based on the waves reflected from the
object. The method includes the steps of: (A) irradiating the
object with a wave to obtain a first received signal that is based
on the wave reflected; (B) calculating a first phase curve showing
a phase shift of the first received signal in a propagation
direction of the wave with respect to a reference signal; (C)
setting a first location in the wave propagating direction and
assigning the measuring point to the first location; (D) defining a
displacement line, which passes one of multiple sample points that
have been set in the wave propagating direction and of which the
gradient is calculated based on the frequency of the reference
signal, the one sample point being located closest to the first
location; (E) irradiating the object with a wave, thereby
calculating a second phase curve, representing a phase shift of the
second received signal with respect to the reference signal; and
(F) finding the intersection between the displacement line and the
second phase curve, adding the distance from the intersection to
the sample point that is closest to the first location to the
location of the measuring point to set a second location, and
defining the second location as a location to which the measuring
point has been displaced. The location of the measuring point is
tracked by performing the steps (B) through (F) all over again with
the second received signal of the step (E) and the second location
of the step (F) substituted for the first received signal and the
first location, respectively.
[0032] In one preferred embodiment, the step (E) includes the steps
of: (E1) calculating the phase difference between the first and
second received signals at the sample point that is located closest
to the first location; (E2) adding the phase difference, calculated
in the step (E1), to the phase at the closest sample point on the
first phase curve, thereby calculating the phase of the second
received signal at that closest sample point; (E3) calculating
phase differences for multiple sample points that are adjacent to
the closest sample point; and (E4) defining either an approximation
line or an approximation curve as the second phase curve based on
the phase that has been calculated in the step (E2) and the phase
difference that has been calculated in the step (E3).
[0033] In yet another preferred embodiment, if the unit of the
distance axis of a distance-phase plane is a length unit, the
gradient of the displacement line is calculated -4.pi.f/C, where f
is the frequency of the reference signal and C is the propagation
velocity of the waves.
[0034] In an alternative preferred embodiment, if the unit of the
distance axis of a distance-phase plane is a receiving time unit,
the gradient of the displacement line is calculated -2.pi.f, where
f is the frequency of the reference signal.
[0035] A location tracking apparatus according to the present
invention includes: a transmitting section for irradiating the
object with a wave; a receiving section for receiving a wave that
has been reflected from the object to generate a received signal;
and a tracking section for tracking the location of a measuring
point that has been set on the object by any of the location
tracking methods described above.
[0036] An ultrasonic diagnostic apparatus according to the present
invention includes: a transmitting section for transmitting an
ultrasonic wave toward an object of measurement using a probe; a
receiving section for receiving a wave that has been reflected from
the object through the probe to generate a received signal; and a
tracking section for tracking the location of a measuring point
that has been set on the object by any of the location tracking
methods described above in cooperation with the transmitting and
receiving sections. The apparatus evaluates at least one of the
shape property and the attribute property of the object based on
the location of the measuring point that has been calculated by the
tracking section.
[0037] In one preferred embodiment, the attribute property is one
of the magnitude of strain, elasticity and viscosity of the
object.
[0038] In another preferred embodiment, the apparatus further
includes an elasticity calculating section that receives a signal
representing a variation in stress applied to the object and that
calculates the elasticity of the object based on the location of
the measuring point that has been detected by the tracking
section.
[0039] In still another preferred embodiment, the object of
measurement is a vascular wall and the signal representing the
variation in stress is a blood pressure waveform.
[0040] In yet another preferred embodiment, the object of
measurement is a vascular wall and the attribute property is a
diagnostic index of arterial sclerosis including at least one of an
intima-media thickness (IMT) and a pulse wave velocity (PWV).
[0041] In yet another preferred embodiment, the object of
measurement is a heart and the shape property is a
contraction/dilation property.
EFFECTS OF THE INVENTION
[0042] According to the location tracking method of the present
invention, even if a number of reflected waves that have come from
multiple sources of reflection are received as superposed waves and
if the phases of the received signals are disturbed, the motion of
the measuring point that has been set in the object can also be
tracked accurately. In addition, the ultrasonic diagnostic
apparatus of the present invention can also be used to accurately
measure an attribute of the subject's tissue such as the strain,
elasticity or viscosity thereof and precisely evaluate the motion
function of the subject's tissue in terms of the shrinkage and
dilation thereof, for example.
BRIEF DESCRIPTION OF DRAWINGS
[0043] FIG. 1 shows a method for tracking a tissue based on the
phase difference of an ultrasonic echo signal.
[0044] FIG. 2(a) is a schematic representation showing how to
calculate the elasticity of a vascular wall and FIG. 2(b) shows how
to calculate the magnitude of strain using a tracking waveform
obtained from a vascular wall.
[0045] FIG. 3 shows a conventional method for tracking the location
of a measuring point based on a phase difference.
[0046] FIG. 4 shows a configuration for an orthogonal detector.
[0047] FIG. 5 shows a first preferred embodiment of a location
tracking method according to the present invention.
[0048] FIG. 6 shows how phase curves change with time.
[0049] FIG. 7 is a flowchart showing the procedure of the location
tracking method of the first preferred embodiment.
[0050] FIG. 8 shows how to correct a phase that is discontinuous in
the distance direction.
[0051] FIG. 9 shows an offset between phase curves.
[0052] FIG. 10 shows an exemplary method of calculating a phase
curve.
[0053] FIG. 11 shows another exemplary method of calculating a
phase curve.
[0054] FIG. 12 shows an exemplary method of locating an
intersection between a phase curve and a displacement line.
[0055] FIG. 13 is a flowchart showing the procedure of a location
tracking method according to the present invention that adopts
digital signal processing.
[0056] FIG. 14 is a flowchart showing the procedure of a location
tracking method according to a second preferred embodiment of the
present invention.
[0057] FIG. 15 illustrates how the procedure shown in FIG. 14 is
carried out.
[0058] FIG. 16 is a flowchart showing the procedure of a simplified
version of the location tracking method of the second preferred
embodiment.
[0059] FIG. 17 illustrates how the procedure shown in FIG. 16 is
carried out.
[0060] FIG. 18 is a flowchart showing the procedure of another
simplified version of the location tracking method of the second
preferred embodiment.
[0061] FIG. 19 illustrates how the procedure shown in FIG. 18 is
carried out.
[0062] FIG. 20 is a block diagram showing the configuration of an
ultrasonic diagnostic apparatus according to the present
invention.
[0063] FIG. 21 shows an example of a picture presented on the
monitor of the ultrasonic diagnostic apparatus shown in FIG.
20.
DESCRIPTION OF REFERENCE NUMERALS
[0064] 100 control section [0065] 101 probe [0066] 102 transmitting
section [0067] 103 receiving section [0068] 104 tomographic image
processing section [0069] 105 tissue tracking section [0070] 106
image synthesizing section [0071] 107 monitor [0072] 108 elasticity
calculating section [0073] 111 blood pressure manometer [0074] 112
blood pressure manometer controlling and blood pressure value
retrieving section [0075] 120 memory [0076] 121 memory [0077] 200
tomographic image [0078] 201 elasticity image [0079] 202
tomographic image reflection intensity scale [0080] 203 elasticity
image scale [0081] 204 biomedical signal waveform
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1
[0082] First, the Problems of the Conventional Method disclosed in
Patent Document No. 1 will be pointed out with reference to FIG. 3,
which shows the results obtained by transmitting a wave (i.e., an
ultrasonic wave in Patent Document No. 1) and by analyzing waves
reflected by two point reflection sources that were arranged in the
direction in which the transmitted wave propagated. The upper
portion of FIG. 3 shows a received signal y1(x) obtained by
transforming a received signal y1(t) into a function of distance by
Equation (1). The received signal y1(t) was generated by converting
a reflected one of a wave that had been transmitted at a time T=0
into an electrical signal. The middle portion of FIG. 3 also shows
a received signal y2(t), obtained from the same point reflection
sources by transmitting the wave all over again .DELTA.T later, as
a function of distance y2(x). The received signals y1(x) and y2(x)
include wave trains w1 and w2, which are waves reflected from the
two reflection sources, respectively. Since the interval between
the two point reflection sources is shorter than the combined
lengths of these wave trains, the wave trains w1 and w2 overlap
with each other. Also, the two point reflection sources are
supposed to be approaching the source of transmission and reception
(i.e., a probe in Patent Document No. 1) at the same velocity. For
that reason, if the transmitting time is supposed to be a reference
time, the wave trains w1 and w2 in the received signal y2(x) are
received earlier than the counterparts in the received signal
y1(x).
[0083] The lower portion of FIG. 3 shows phases .theta.1(x) and
.theta.2(x) obtained by subjecting these two received signals y1(x)
and y2(x) to orthogonal detection by using the detector shown in
FIG. 4 and by calculating the arctangent of the complex received
signals I(x) and Q(x), which are the outputs of the detector. As
the reference frequencies of the orthogonal detection, the carrier
frequencies of the received signals are used. Also, the phases
obtained by the orthogonal detection are corrected by adding .+-.2
.pi. (where n is a positive integer) thereto such that the phases
.theta.n(x) are continuous with each other in the distance
direction. These .theta.n(x) will be referred to herein as "phase
curves".
[0084] According to the method disclosed in Patent Document No. 1,
the phase difference Lie between these two phase curves at the same
distance is subjected to the calculation of Equation (2) to obtain
the magnitude of displacement .DELTA.X, which is then added to the
previous location X as in Equation (3), thereby figuring out a
location to be tracked. For example, a distance X1' that a
measuring point will travel in .DELTA.T if a distance X1 is set for
a received signal of the wave that has been transmitted at the time
T=0 is calculated by substituting a phase difference
.DELTA..theta.1 at the distance X1 into Equation (2) to obtain the
magnitude of displacement .DELTA.X1 and by adding this magnitude of
displacement .DELTA.X1 to X1. A distance X3' that a measuring point
will travel in .DELTA.T if a distance X3 is set for the received
signal can also be figured out by performing similar
calculations.
[0085] The magnitudes of displacement .DELTA.X1 and .DELTA.X3 of
the measuring points at the distances X1 and X3 in the wave trains
w1 and w3 shown in FIG. 3, where a single wave train prevails, can
be calculated accurately by this method. That is to say, the
locations of these measuring points can be tracked sequentially
because the phases match with each other within the wave trains w1
and w2. However, where these two wave trains overlap with each
other, a measuring point at a distance X2 that has been set for the
received signal of a wave transmitted at the time T=0 in FIG. 3,
for example, cannot be tracked accurately. This is because the
degree of overlap between these two wave trains changes with the
distance and therefore the phases are not flat and also because the
displacement of an object in the wave propagating direction is not
represented only by the increase and decrease of phases if the
received signal is transformed into a distance-phase plane. For
example, as shown in the lower portion of FIG. 3, the phase curve
.theta.2(x) shifts not only upward but also leftward with respect
to the phase curve .theta.1(x). That is why the phase difference
.DELTA..theta.2 is found to be greater than the phase differences
.DELTA..theta.1 and .DELTA..theta.3, and the magnitude of
displacement .DELTA.X2 of the distance X2 is calculated a
relatively large value. In FIG. 3, as the object is coming toward
the source of transmission and reception, the phase curve
.theta.2(x) shifts upper-leftward with respect to the phase curve
.theta.1(x). If the object is going away from the source of
transmission and reception, however, the phase curve .theta.2(x)
will shift lower-rightward. In addition, since the phase of the
wave train w2 is ahead of that of w1, the curve rises rightward in
the lower portion of FIG. 3. On the other hand, if the phase of the
wave train w2 is behind that of w1, the curve may fall rightward in
the lower portion of FIG. 3. In that case, the magnitude of
displacement .DELTA.X2 is calculated a relatively small value. As
described above, the measuring point at the distance X2 in the
received signal of a wave that has been transmitted at the time T=0
cannot be tracked properly. That is to say, a tracking error is
generated.
[0086] According to the present invention, such a tracking error
can be reduced. Hereinafter, the location tracking method of the
present invention will be described with reference to FIG. 5. The
location tracking method of the present invention utilizes the fact
that if the received signal is transformed into a distance-phase
plane, the wave shift of the object in the transmitting and
receiving direction is represented not just by the increase and
decrease of the phase but also by those of the distance and that
these variations are produced in conjunction with each other. More
specifically, the magnitude of wave shift of the object in the
transmitting and receiving direction during .DELTA.T, i.e., the
magnitude of shift between the wave trains of two received signals
that have been transmitted and received at an interval of .DELTA.T,
and the phase shift during .DELTA.T, obtained by subjecting the
received signals to an orthogonal detection, satisfy the relation
represented by Equation (2), which can be modified into the
following Equation (6).
.DELTA..theta./.DELTA.X=-4.pi.f/C (6)
[0087] The upper, middle and lower portions of FIG. 5 show the
received signal y1(x), the received signal y2(x) and the phase
curves .theta.1(x), .theta.2(x), respectively, which are produced
under the same conditions as in FIG. 3. The magnitude of shift
between the received signals should satisfy the relation
represented by Equation (6). Therefore, if the initial location of
a measuring point is set on the received signal of a wave that has
been transmitted at the time T=0, then the displacement of the
measuring point at the distance X1 is represented by the line,
which passes (X1, .theta.1(X1)) on the distance-phase plane shown
in the lower portion of FIG. 5 and of which the gradient is given
by Equation (6) (i.e., the line represented by the following
Equation (7)). Thus, the displacement of the measuring point X1 at
the distance X1 is represented by the line given by the following
Equation (7).
.theta.=-4.pi.f(x-X1)/C+.theta.1(X1) (7)
[0088] In the Equation (7), f is the frequency of a reference
signal used in orthogonal detection. This line will be referred to
herein as a "displacement line".
[0089] Thus, the distance X1' that the measuring point travels in
the wave propagating direction in .DELTA.T is the distance at the
intersection between the displacement line given by Equation (7)
and the phase curve .theta.2(x). The distance X'' of the next
destination is the distance at the intersection between the
displacement line given by Equation (7) and a phase curve
.theta.3(x) (not shown). The same statement applies to distances X2
and X3, too. As can be seen FIG. 5, the peak portions of the
received signal waveform can be tracked accurately irrespective of
the degree of overlap between the wave trains.
[0090] According to the conventional method, the magnitude of
displacement is calculated by Equation (2) using the phase
difference at the same distance. In that case, however, if the
waves overlapped with each other to disturb phases, the magnitude
of displacement would contain some errors. On the other hand,
according to the location tracking method of the present invention,
an initial location is set, and a displacement line representing
the displacement of the initial location as given by Equation (7)
is plotted on a distance-phase plane defining a phase curve. For
that reason, even if the waves overlap with each other to disturb
the phases, the location of the measuring point displaced can be
calculated as the intersection between the phase curve and the
displacement line.
[0091] FIG. 6 shows the shifts of phase curves .theta.n(x) in a
situation where the source of reflection is coming toward the
source of transmission and reception at a constant velocity under
the same condition as in FIG. 3 and where the waves are transmitted
and received at an interval of .DELTA.T. FIG. 6 also shows the
displacement lines of measuring points in a situation where initial
locations are set at distances X1, X2 and X3. The initial location
of a measuring point is set by the distance and phase that are
defined on the phase curve .theta.1(x) at the transmitting time
T=0. As can be seen from the line representing the displacement of
the measuring point set at the distance X2, the oblique phases can
be tracked accurately, and therefore, overlapping portions between
the waves of received signals can be tracked. Thus, according to
the location tracking method of the present invention, even if
mutually overlapping echoes are received from multiple sources of
reflection and if the phases of the received signals are disturbed,
the displacement of the measuring point can also be tracked
accurately.
[0092] Also, according to the location tracking method of the
present invention, the magnitudes of displacements are not added
together one after another unlike the method disclosed in Patent
Document No. 1, and therefore, the errors are never accumulated at
the location to be tracked. The reference frequency f of the
orthogonal detection is usually set in the vicinity of the center
frequency of a transmitted pulse or the carrier frequency of a
received signal. However, according to the present invention, the
reference frequency f can be set freely and does not have to be the
vicinity of the center frequency of a transmitted pulse or the
carrier frequency of a received signal. Furthermore, according to
the present invention, the phase just needs to be calculated for a
reference signal with a single predetermined frequency f and the
phase detection means does not have to be orthogonal detection. For
example, the phase may also be figured out by a Fourier transform
with the regions divided. In Equation (7), the unit in the distance
direction is supposed to be a length unit. Alternatively, the unit
may also be a time unit that is defined by Equation (1) with
respect to the transmitting time. In that case, if the initial
location is t1, the displacement line given by Equation (7) may be
represented by the following Equation (8).
.theta.=-2.pi.f(t-t1)+.theta.1(t1) (8)
[0093] Hereinafter, a specific procedure of the location tracking
method of the present invention will be described with reference to
FIGS. 5, 7, 8 and 9. First, in Step S301, an object is irradiated
with a wave and the wave reflected from the object is converted
into an electrical signal, thereby obtaining a received signal
y1(x). Next, in Step S302, the received signal y1(x) is subjected
to an orthogonal detection using a reference signal with a single
frequency f to find the phase of the received signal y1(x) with
respect to the reference signal. Subsequently, in Step S303, the
arctangent of the resultant complex received signal is calculated,
thereby figuring out a phase curve .theta.1(x) representing its
phase in the wave propagating direction with respect to the
reference signal. The phase curve obtained in this process step may
be discontinuous between -.pi. and .pi. as shown in FIG. 8. That is
why as indicated by the dashed line in FIG. 8, .+-.2.pi. is added,
thereby correcting the phase curve into a continuous one. Also, to
track the location of the object, the object is repeatedly
irradiated with a plurality of waves to figure out multiple phase
curves as will be described later. For that reason, .+-.2n.pi.
(where n is a positive integer) is added to the entire phase curve
such that a phase curve and its previous phase curve have a phase
difference approximately within .+-..pi. as shown in FIG. 9. If the
previous phase curve is .theta.1(x) as shown in FIG. 9, the phase
curve .theta.2'(x) to be obtained now should have a phase
difference of at least .pi. with respect to .theta.1(x). That is
why -2.pi. is added to (i.e., 2.pi. is subtracted from) the entire
.theta.2'(x) to obtain a proper phase curve .theta.2(x).
[0094] Next, in Step S304, it is determined whether the location of
the measuring point should be initialized or not. More
particularly, if a signal instructing that the tracking location of
the measuring point be initialized has been detected, then the
measuring point is assigned to an initial location in the received
signal in Step S307. Even if the received signal is the first one
that has ever been received, the processing step S307 is also
carried out in response to that signal instructing that the
tracking location be initialized. Either a single measuring point
or a plurality of measuring points may be set. For example, in FIG.
5, initial locations X1, X2 and X3 are set at distances of
approximately 3.75 mm, 4.1 mm and 4.5 mm, respectively, and
measuring points are assigned to all of these three locations.
[0095] Thereafter, in Step S308, a displacement line (given by
Equation (7)) that passes the initial location on the phase curve
.theta.1(x) and that is defined by the frequency f of the reference
signal and the propagation velocity C of the wave is determined. In
FIG. 5, for example, three lines that pass the initial locations
X1, X2 and X3 on the phase curve .theta.1(x) and that have a
gradient -4.pi.f/C are determined.
[0096] Next, the processing steps S301, S302 and S303 are carried
out all over again. Specifically, the object is irradiated with
another wave, a received signal is generated based on the wave
reflected, and a phase curve .theta.2(x) representing the phase of
the received signal in the wave propagating direction with respect
to the reference signal is obtained. Unless the signal instructing
that the tracking location of the measuring point be initialized
has been received, the process advances from Step S304 to Step
S305, in which the intersection between the phase curve .theta.2(x)
just obtained and the displacement line is located. Then, in Step
S306, the intersection found is defined as the destination of the
measuring point. That is to say, the new location of the measuring
point is determined.
[0097] After that, the same processing steps S301, S302, S303,
S304, S305 and S306 are carried out all over again to irradiate the
object with another wave, obtain another phase curve, find an
intersection between a displacement line and the phase curve, and
locate the measuring point repeatedly.
[0098] Also, the signal instructing that the tracking location of
the measuring point be initialized is output at an appropriate
interval. Thus, every time the signal instructing that the tracking
location of the measuring point be initialized is detected, the
location of the measuring point is initialized and a displacement
line that passes the initial location is obtained.
[0099] In measuring the elasticity of a vascular wall as disclosed
in Patent Document No. 2, the signal instructing that the tracking
location of a measuring point be initialized may be a pulse sync
signal represented by R waves of an electrocardiograph (ECG), for
example. Also, according to Patent Document No. 2, multiple initial
locations of measuring points are set at regular intervals in the
distance direction, which is on the acoustic line of the ultrasonic
wave. By repeatedly performing such a procedure, the subject's
tissue can be tracked accurately.
[0100] Hereinafter, a specific phase curve calculating method will
be described. If the location is tracked by the location tracking
method of the present invention, an actual apparatus may sample the
received signal and process it as a digital signal either before or
after the orthogonal detection. For that reason, the resultant
phase curve will not be a continuous curve but actually a group of
phase data representing the phase of the received signal with
respect to the reference signal at multiple sample points that have
been set at predetermined intervals in the wave propagating
direction. In general, those sample points are fixed and never move
while the location of the object is being tracked.
[0101] First, as shown in FIG. 10, if a signal instructing that the
tracking location of the measuring point be initialized has been
detected or if the phase curve .theta.1(x) should be calculated for
the signal that has been received for the very first time, the
received signal is subjected to an orthogonal detection and the
arctangent of the resultant complex received signal is calculated,
thereby finding the phases of the received signal with respect to
sample points Xa, Xb, Xc and Xd. In FIG. 10, the open circles
.largecircle. on the phase curve .theta.1(x) indicate the sample
points. As described above, the phase curve .theta.1(x) actually
has data only at those sample points, i.e., is actually a group of
phase data.
[0102] To obtain a phase curve .theta.2(x) based on a signal that
has been received for the second time, phase differences
.DELTA..phi.a, .DELTA..phi.b, .DELTA..phi.c and .DELTA..phi.d
between the phases .theta.1(Xa), .theta.1(Xb), .theta.1(Xc) and
.theta.1(Xd) of the first group of phase data, calculated based on
the first received signal and representing a phase curve, and the
phases of the second received signal are figured out. The phase
differences can be figured out by calculating the arctangent of the
complex conjugate product of the first and second complex received
signals that have already been subjected to the orthogonal
detection. Next, as pointed by the arrows in FIG. 10, the phase
differences .DELTA..phi.a, .DELTA..phi.b, .DELTA..phi.c and
.DELTA..phi.d thus obtained are added to the phases .theta.1(Xa),
.theta.1(Xb), .theta.1(Xc) and .theta.1(Xd) of the first group of
phase data that have been calculated based on the first received
signal and that represent a phase curve. As a result, a second
group of phase data, representing a phase curve .theta.2(x)
consisting of .theta.2(Xa), .theta.2(Xb), .theta.2 (Xc) and
.theta.2(Xd), can be obtained. In this processing step, if the
displacement of the object is partially quick, then the phase may
become discontinuous between -.pi. and .pi.. In that case,
.+-.2.pi. is added to correct the phase into a continuous one as
already described with reference to FIGS. 8 and 9. Likewise, to
obtain a third group of phase data, the phase differences between
the second and third received signals are added to the second group
of phase data. The same statement applies to the other groups of
phase data, too.
[0103] Alternatively, the phase curve .theta.2(x) may also be
figured out by another method. To figure out a phase curve
.theta.2(x) based on the second received signal, a phase difference
between the phase at any of the sample points of the first group of
phase data obtained based on the first received signal and the
phase at that sample point on the second received signal is
calculated as shown in FIG. 11. For example, a phase difference
.DELTA..phi.a is calculated at a sample point Xa. Next, the phase
difference .DELTA..phi.a is added to the phase .theta.1(Xa) of the
first group of phase data at the sample point Xa, thereby obtaining
the phase .theta.2(Xa) at the sample point Xa of the phase curve
.theta.2(x) based on the second received signal.
[0104] Subsequently, phase differences .DELTA..phi.b',
.DELTA..phi.c' and .DELTA..phi.d' between two adjacent samples
points on the phase curve .theta.2(x) are calculated and are
sequentially added to the phase .theta.2 (Xa) at the sample point
Xa on the phase curve .theta.2(x), thereby obtaining a second group
of phase data showing the phase curve .theta.2(x) that consists of
.theta.2(Xa), .theta.2(Xb), .theta.2(Xc) and .theta.2(Xd).
Likewise, to obtain a third group of phase data, a phase difference
between the second and third received signals is calculated at any
of the sample points, third phase data at that point is obtained,
and then the phase difference between adjacent sample points of the
third received signal is added, thereby calculating the third group
of phase data. The same statement applies to the other groups of
phase data.
[0105] Next, an exemplary method of locating the intersection
between a phase curve and a displacement line will be described
with reference to FIG. 12. As described above, the phase curve is
actually a group of phase data consisting of only the phases at
sample points. If the signal instructing that the tracking location
of a measuring point be initialized is detected when the phase
curve .theta.1 is calculated, measuring points are set at
initialized locations X1 and X2. In this case, if the initialized
location (e.g., X1) agrees with one of the sample points, a
displacement line #1 that passes (X1, .theta.1(X1)) on a
distance-phase plane is calculated.
[0106] On the other hand, if the initialized location (e.g., X2)
does not agree with any of the sample points, then a line is drawn
tentatively on the supposition that the phase changes linearly
between the previous and following sample points Xd and Xe (shown
on the left- and right-hand sides of X2 in FIG. 12), and the phase
at the X2 location on that line is obtained, thereby calculating a
phase line #2 that passes the location on a distance-phase
plane.
[0107] After a group of phase data representing the phase curve
.theta.2(x) has been obtained based on the next received signal,
the intersection between the displacement line and the phase curve
.theta.2(x) is located. Since the sample points are not continuous
on the phase curve .theta.2(x) in this case, the intersection
between the phase curve and the displacement line does not agree
with any of the sample points in most cases. That is why a line is
tentatively drawn on the supposition that the phase changes
linearly between sample points, and the intersection between that
line and the displacement line is supposed to be the destination.
For example, as shown in FIG. 12, a line is tentatively drawn
between the two sample points Xa and Xb on the phase curve
.theta.2(x), and the intersection X1' between that line and the
displacement line #1 is located. In the same way, a line is
tentatively drawn between the two sample points Xd and Xe on the
phase curve .theta.2(x), and the intersection X2' between that line
and the displacement line #2 is located. As shown in FIG. 12, the
magnitude of displacement .DELTA.X1 of the measuring point X1 is
greater than that .DELTA.X2 of the measuring point X2. That is to
say, this object has expanded. As can be seen, according to the
present invention, not just when the overall object travels
horizontally as shown in FIG. 5 but also when the object compresses
or expands in the wave propagating direction, the location of each
measuring point can be tracked accurately.
[0108] It should be noted that the interpolation method for
approximating a phase curve based on a group of phase data does not
have be such a linear interpolation but may also be any other
interpolation method that uses a curve or a spline curve by a
minimum square method, for example.
[0109] Hereinafter, a location tracking method according to the
present invention, including such digital signal processing, will
be described with reference to FIGS. 12 and 13. First, in Step
S351, an object is irradiated with a wave and the wave reflected
from the object is converted into an electrical signal, thereby
obtaining a received signal y1(x). Next, in Step S352, the received
signal y1(x) is subjected to an orthogonal detection using a
reference signal with a single frequency f to find the phase of the
received signal y1(x) with respect to the reference signal. By
making sampling either before or after the orthogonal detection,
the resultant complex received signal turns into a group of digital
complex data. The rest of the signal processing is performed
digitally.
[0110] Subsequently, in Step S353, a group of phase data
.theta.1(x) is calculated based on the group of complex data thus
obtained. If no group of phase data has been obtained in the
previous processing step, the arctangent of the group of complex
data is calculated, thereby obtaining a group of phase data
representing phases at respective sample points. On the other hand,
if a group of phase data has been obtained in the previous
processing step, another group of phase data is figured out by the
method that has already been described with reference to FIG. 10 or
11.
[0111] Next, in Step S354, it is determined whether the location of
the measuring point should be initialized or not. More
particularly, if a signal instructing that the tracking location of
the measuring point be initialized has been detected, then the
measuring point is assigned to an initial location X1 in Step S358.
Even if the received signal is the first one that has ever been
received, the processing step S358 is also carried out in response
to that signal instructing that the tracking location be
initialized. Either a single measuring point or a plurality of
measuring points may be set. Subsequently, in Step S359, the phase
value of the initial location, which is the location of the
measuring point on the group of phase data .theta.1(x), is
calculated by the method described above. Thereafter, in Step S360,
a displacement line (given by Equation (7)) that passes the initial
location, which is the location of the measuring point on the group
of phase data .theta.1(x), and that is defined by the frequency f
of the reference signal and the propagation velocity C of the wave
is determined.
[0112] The group of phase data .theta.1(x) thus obtained is stored
as the previous group of phase data in a memory in Step S361. Also,
the group of complex data obtained by the orthogonal detection is
stored as the previous group of complex data in the memory in Step
S362.
[0113] Next, the processing steps S351, S352 and S353 are carried
out all over again. Specifically, the object is irradiated with
another wave, a received signal is generated based on the wave
reflected, and a group of phase data .theta.2(x) representing the
phase of the received signal in the wave propagating direction with
respect to the reference signal is obtained. The group of phase
data .theta.2 is figured out based on the group of phase data
.theta.1(x) by the method that has already been described with
reference to FIG. 10 or 11. Unless the signal instructing that the
tracking location of the measuring point be initialized has been
received, the process advances from Step S354 to Step S355.
[0114] In Step S355, the intersection between the group of phase
data .theta.2(x) and the displacement line is located just as
described above. Then, in Step S356, the intersection thus found is
defined as the destination of the measuring point. That is to say,
the new location of the measuring point is determined. The group of
phase data .theta.2(x) thus obtained is stored as the previous
group of phase data in the memory in Step S361. Also, the group of
complex data is stored as the previous group of complex data in the
memory in Step S362.
[0115] After that, the same processing steps S351, S352, S353,
S354, S355, S356, S361 and S362 are carried out all over again to
irradiate the object with another wave, obtain another group of
phase data, find an intersection between a displacement line and
the group of phase data, and locate the measuring point repeatedly.
Also, the signal instructing that the tracking location of the
measuring point be initialized is output at an appropriate
interval. Thus, every time the signal instructing that the tracking
location of the measuring point be initialized is detected, the
location of the measuring point is initialized and a displacement
line that passes the initial location is obtained.
Embodiment 2
[0116] According to the method of the first preferred embodiment
described above, a displacement line is calculated only when the
location of a measuring point should be initialized. That is to
say, the displacement line is calculated based on a phase curve
when the location of the measuring point is initialized. This means
that to calculate the tracking location based on the intersection
between the displacement line and the phase curve, the phase
relation between the newest phase curve and the phase curve when
the location of the measuring point was initialized needs to be
maintained. That is why either by sequentially adding the phase
difference at every sample point to the previous group of phase
data as shown in FIG. 10 or adding the phase difference at one
sample point to the previous sample point to calculate a reference
sample point as shown in FIG. 11, the phase relation between the
newest phase curve and the phase curve when the location of the
measuring point was initialized is maintained. In other words,
there are a number of phase curves between the newest phase curve
and the phase curve when the location of the measuring point was
initialized, and the accumulation of phase differences between
those phase curves shows the phase relation between the newest
phase curve and the phase curve when the location of the measuring
point was initialized.
[0117] On the other hand, according to this preferred embodiment,
every time a phase curve is calculated, a displacement line is
calculated. Hereinafter, a location tracking method according to
this preferred embodiment will be described with reference to FIGS.
14 and 15. In the following example, transmission of a wave and
reception of a reflected wave are repeatedly performed, one of the
resultant received signals that has just been obtained as a result
of the newest transmission and reception will be referred to herein
as a "second received signal" and another received signal that was
obtained as a result of the previous transmission and reception a
"first received signal", respectively. The same naming rule will
also apply to complex received signals, phase curves and so on
obtained by detecting the received signals. If the signal
processing is carried out digitally, the complex received signals
and phase curves are groups of complex data and groups of phase
data, respectively.
[0118] First, in Step S371, an object is irradiated with a wave and
the wave reflected from the object is converted into an electrical
signal, thereby obtaining a second received signal. Next, in Step
S372, the second received signal is subjected to an orthogonal
detection using a reference signal with a single frequency f to
find the phase of the second received signal with respect to the
reference signal. In this manner, a second complex received signal
is obtained. Since digital signal processing is carried out in this
preferred embodiment, sampling is performed either before or after
the orthogonal detection, and the resultant second complex received
signal is a second group of digital complex data.
[0119] Subsequently, in Step S373, it is determined whether the
location of the measuring point should be initialized or not. More
particularly, if a signal instructing that the tracking location of
the measuring point be initialized has been detected, then the
measuring point is assigned to an initial location in Step S380.
Even if the received signal is the first one that has ever been
received, the processing step S380 is also carried out in response
to that signal instructing that the tracking location be
initialized. In FIG. 15, the initial location of the measuring
point is set at the distance X1. Next, Step S381 is carried out to
store the second group of complex data as a first group of complex
data in a memory.
[0120] Next, the processing steps S371 and S372 are carried out all
over again. Specifically, the object is irradiated with another
wave, a second received signal is generated based on the wave
reflected, and the second received signal is subjected to the
orthogonal detection to obtain a second group of complex data.
Unless the signal instructing that the tracking location be
initialized has been received, the process advances from Step S373
to Step S374.
[0121] In Step S374, the arctangent of the first group of complex
data stored in the memory is calculated, thereby obtaining a first
group of phase data (or a first phase curve). In FIG. 15, the first
group of phase data is identified by .theta.1(x). Next, in Step
S375, the phase .theta.1(X1) at the location X1 on the first group
of phase data is calculated. Specifically, a line passing the
sample points .theta.1(Xb) and .theta.1(Xc) before and after the
location X1 is drawn tentatively and the phase .theta.1(X1) at X1
is calculated by linear interpolation.
[0122] Thereafter, in Step S376, a displacement line L that passes
the measuring point (X1, .theta.1(X1)) on the first group of phase
data and that has a gradient of -4.pi.f/C is obtained on a
distance-phase plane. Next, in Step S377, a second group of phase
data .theta.2(x) is calculated based on the first group of phase
data .theta.1(x) as already described for the first preferred
embodiment with reference to FIG. 10 or 11.
[0123] Subsequently, in Step S378, the intersection between the
second group of phase data .theta.2(x) and the displacement line is
located just as already described with reference to FIG. 12. The
intersection is identified by (X1', .theta.2(X1')) in FIG. 15.
Next, in Step S379, the intersection thus found is defined as the
destination of the measuring point. That is to say, the measuring
point moves from X1 to X1'.
[0124] Thereafter, in Step S381, the second group of complex data
is stored as the first group of complex data in the memory.
[0125] After that, the same processing steps S371 through S379 and
S381 are carried out all over again to irradiate the object with
another wave, generate a second received signal based on the wave
reflected, subject the second received signal to an orthogonal
detection and calculate the second group of complex data
repeatedly. In Step S374, the arctangent of the first group of
complex data stored in the memory is calculated, thereby obtaining
a first group of phase data (or a first phase curve). In FIG. 15,
the first group of phase data is identified by .theta.1'(x).
[0126] The first group of complex data that has been stored in the
memory was formerly the second group of complex data that was used
to calculate the previous second group of phase data .theta.2(x).
However, the previous second group of phase data .theta.2(x) has
been calculated based on the first group of phase data .theta.1(x)
by the method shown in FIG. 10 or 11, whereas the first group of
phase data .theta.1'(x) is obtained by calculating the arctangent
of the first group of complex data stored in the memory. That is
why these two groups may have different phases and the first group
of phase data .theta.1'(x) does not always agree with the second
group of phase data .theta.2(x).
[0127] Next, in Step S375, the phase .theta.1'(X1') at the location
X1' on the first group of phase data .theta.1'(x) is calculated.
Specifically, a line passing the sample points .theta.1'(Xb) and
.theta.1'(Xc) before and after the location X1' is drawn
tentatively and the phase .theta.1'(X1') at X1' is calculated by
linear interpolation.
[0128] Thereafter, in Step S376, a displacement line L' that passes
the measuring point (X1', .theta.1'(X1')) on the first group of
phase data .theta.1'(x) and that has a gradient of -4.pi.f/C is
obtained on a distance-phase plane. Next, in Step S377, a second
group of phase data .theta.2'(x) is calculated based on the first
group of phase data .theta.1'(x) as described above.
[0129] Subsequently, in Step S378, the intersection between the
second group of phase data .theta.2(x) and the displacement line is
located just as already described with reference to FIG. 12. The
intersection is identified by (X1'', .theta.2'(X1'')) in FIG. 15.
Next, in Step S379, the intersection thus found is defined as the
destination of the measuring point. That is to say, the measuring
point moves from X1' to X1''.
[0130] As described above, according to this preferred embodiment,
each displacement line is re-calculated based on the previous phase
curve. That is why there is no need to define the phase relation
between the newest phase curve and the other phase curves that
precede the previous one. As a result, it is possible to
substantially avoid a situation where noise or error that has
occurred halfway through a series of processing will have an
unbeneficial effect for the rest of the processing.
[0131] Hereinafter, a simplified version of the location tracking
method according to this preferred embodiment will be described
with reference to FIGS. 16 and 17. In the following example,
transmission of a wave and reception of a reflected wave are also
repeatedly performed, one of the resultant received signals that
has just been obtained as a result of the newest transmission and
reception will be referred to herein as a "second received signal"
and another received signal that was obtained as a result of the
previous transmission and reception a "first received signal",
respectively. The same naming rule will also apply to complex
received signals, groups of complex data, phase curves, groups of
phase data and so on obtained by detecting the received signals.
First, in Step S310, an object is irradiated with a wave and the
wave reflected from the object is converted into an electrical
signal, thereby obtaining a second received signal. Next, in Step
S311, the second received signal is subjected to an orthogonal
detection using a reference signal with a single frequency f to
find the phase of the second received signal with respect to the
reference signal. In this manner, a second group of complex data is
obtained.
[0132] Subsequently, in Step S312, it is determined whether the
location of the measuring point should be initialized or not. More
particularly, if a signal instructing that the tracking location of
the measuring point be initialized has been detected, then the
measuring point is assigned to an initial location in Step S313.
Even if the received signal is the first one that has ever been
received, the processing step S313 is also carried out in response
to that signal instructing that the tracking location be
initialized. In FIG. 17, the initial location of the measuring
point is set at the distance X1. Next, Step S321 is carried out to
store the second group of complex data as a first group of complex
data in a memory.
[0133] Next, the processing steps S310, S311 and S312 are carried
out all over again. Specifically, the object is irradiated with
another wave, a second received signal is generated based on the
wave reflected, and the second received signal is subjected to the
orthogonal detection to obtain a second group of complex data.
Unless the signal instructing that the tracking location be
initialized has been received, the process advances from Step S312
to Step S314.
[0134] Next, in Step S314, the phase .theta.1(X1) at the location
X1 on the first group of phase data is calculated based on the
first group of complex data. Specifically, first, the arctangent of
the group of complex data between the previous and following sample
points Xb and Xc is calculated to obtain phase data .theta.1(Xb)
and .theta.1(Xc). Next, a line is drawn tentatively between
.theta.1(Xb) and .theta.1(Xc) and the phase .theta.1(X1) at X1 is
calculated by linear interpolation. In this case, the phase
.theta.1(Xc) at the sample point Xc that is closest to the location
X1 of the measuring point may set equal to zero. Thereafter, in
Step S315, a displacement line that passes (X1, .theta.1(X1)) and
that has a gradient of -4.pi.f/C is obtained on a distance-phase
plane.
[0135] Subsequently, in Step S316, the phase difference
.DELTA.between the phase data .theta.1(x) and the phase data
.theta.2(x) or .theta.2'(x), which are the values of the first and
second received signals at the sample point Xc that is closest to
the measuring point location X1, is calculated. Specifically, the
phase difference .DELTA..phi. is figured out by calculating the
arctangent of a complex conjugate product of the first and second
groups of complex data at the sample point Xc. If the phase
difference .DELTA..phi. is positive as in Steps S317, S318 and
S318', the destination of the measuring point is located in the
direction in which the distance decreases. In the example shown in
FIG. 17, .theta.2(x) has such a pattern, and therefore, the
intersection is searched for leftward from the measuring point X1.
As shown in FIG. 17, the phase difference .DELTA..phi.1 of the
second group of phase data between the sample points Xc and Xb is
calculated. Specifically, the phase difference .DELTA..phi.1 is
figured out by calculating the arctangent of a complex conjugate
product of the second complex data at the sample points Xb and Xc.
By adding the phase difference .DELTA..phi. to the phase
.theta.1(Xc) of the first group of phase data at the sample point
Xc, the phase .theta.2(Xc) of the second group of phase data at the
sample point Xc can be obtained. Also, by adding the phase
difference .DELTA..phi.1, the phase .theta.2(Xb) at the sample
point Xb can be obtained.
[0136] A line is tentatively drawn between .theta.2(Xb) and
.theta.2(Xc) and an intersection between that line and the
displacement line is found. If there is no intersection between the
sample points Xb and Xc, then the phase difference .DELTA..phi.2
between the sample points Xb and Xa of the second received signal
is figured out and added to the phase .theta.2(Xb), thereby
calculating the phase .theta.2(Xa) at the sample point Xa.
Specifically, a line is tentatively drawn between .theta.2(Xa) and
.theta.2(Xb) and an intersection between that line and the
displacement line is located. If there is no intersection between
Xa and Xb, then the same type of processing is performed in the
direction in which the distance further shortens, thus finding an
intersection X1'. In Step S320, the location of the intersection
X1' thus found is defined as the location of the next measuring
point.
[0137] If the phase difference .DELTA..phi. is negative as in Steps
S319 and S319', the destination of the measuring point is located
in the direction in which the distance increases. In the example
shown in FIG. 17, .theta.2'(x) has such a pattern, and therefore,
the second group of phase data .theta.2'(x) is calculated between
Xb and Xc and then between Xc and Xd, and the intersection is
searched for rightward from the measuring point X1. Then, in Step
S320, the location of the intersection X1' thus found is defined as
the location of the next measuring point.
[0138] Next, the processing step S321 is carried out and the second
group of complex data is stored as a first group of complex data in
the memory. By adopting such a method, the destination of the
measuring point can be located by calculating only required phases
for just a portion of a phase curve according to the sign of the
phase difference .DELTA..phi. without calculating the phase at
every sample point as shown in FIG. 7. As a result, the
computational complexity can be reduced. Among other things,
calculation of an arctangent, which requires a lot of computations,
can be omitted.
[0139] According to the procedure that has just been described with
reference to FIGS. 16 and 17, data at some of the sample points on
a phase curve is figured out following the procedure shown in FIG.
11. If the first phase curve .theta.1(x) has been obtained to a
certain extent, then the data at those sample points on the phase
curve may be figured out following the procedure shown in FIG. 10
instead of that shown in FIG. 11.
[0140] Hereinafter, a further simplified version of the location
tracking method that has already been described with reference to
FIGS. 16 and 17 will be described with reference to FIGS. 18 and
19. In the following example, transmission of a wave and reception
of a reflected wave are also repeatedly performed, one of the
resultant received signals that has just been obtained as a result
of the newest transmission and reception will be referred to herein
as a "second received signal" and another received signal that was
obtained as a result of the previous transmission and reception a
"first received signal", respectively. The same naming rule will
also apply to complex received signals, groups of complex data,
phase curves, groups of phase data and so on obtained by detecting
the received signals. First, in Step S330, an object is irradiated
with a wave and the wave reflected from the object is converted
into an electrical signal, thereby obtaining a second received
signal. Next, in Step S331, the second received signal is subjected
to an orthogonal detection using a reference signal with a single
frequency f to find the phase of the second received signal with
respect to the reference signal. In this manner, a second group of
complex data is obtained.
[0141] Subsequently, in Step S332, it is determined whether the
location of the measuring point should be initialized or not. More
particularly, if a signal instructing that the tracking location of
the measuring point be initialized has been detected, then the
measuring point is assigned to an initial location in Step S333.
Even if the received signal is the first one that has ever been
received, the processing step S333 is also carried out in response
to that signal instructing that the tracking location be
initialized. In FIG. 19, the initial location of the measuring
point is set at the distance X1. Next, Step S339 is carried out to
store the second group of complex data as a first group of complex
data in a memory.
[0142] Next, the processing steps S330, S331 and S332 are carried
out all over again. Specifically, the object is irradiated with
another wave, a second received signal is generated based on the
wave reflected, and the second received signal is subjected to the
orthogonal detection to obtain a second group of complex data.
Unless the signal instructing that the tracking location be
initialized has been received, the process advances from Step S332
to Step S334.
[0143] Thereafter, in Step S334, a displacement line, which passes
the sample point (Xc, .theta.1(Xc)) that is closest to the
measuring point location X1 on the first group of phase data and
which has a gradient of -4.pi.f/C, is obtained on a distance-phase
plane. Next, a second group of phase data is calculated based on
the second group of complex data and an intersection with the
displacement line is calculated. Subsequently, in Step S335, the
phase difference .DELTA..phi. between the first and second groups
of phase data at the sample point Xc that is closest to the
location X1 is obtained. Then, in Step S336, the phase difference
.DELTA..phi.2 between the sample points Xc and Xb and the phase
difference .DELTA..phi.1 between the sample points Xc and Xd are
calculated based on the second group of phase data. After that, an
approximation line of the second group of phase data .theta.2(x) in
the vicinity of Xc is figured out based on the phase differences
.DELTA..phi., .DELTA..phi.1 and .DELTA..phi.2 by a minimum square
method, for example.
[0144] Next, in Step S337, an intersection between that
approximation line and the displacement line is located. Then, in
Step S338, the distance .DELTA.X between the intersection and the
sample point Xc that is closest to the measuring point location X1
is calculated as the magnitude of displacement. By adding .DELTA.X
to the initial location X1, the next location X1' of the measuring
point can be obtained. Next, Step S339 is performed to store the
second group of complex data as a first group of complex data in
the memory. By repeatedly performing these processing steps S330,
S331, S332, S334 through S338 and S339, the location of the
measuring point can be tracked with the computational complexity
further reduced. Among other things, calculation of an arctangent,
which requires a lot of computations, can be omitted.
[0145] The approximation line does not have to be calculated by the
minimum square method using three points but may also be calculated
based on two points or more than three points. Besides, not just
the linear approximation but also a high-order curve or any other
curve may be adopted as well. Furthermore, phases may be
selectively used according to the sign of .DELTA..phi..
Specifically, if .DELTA..phi. is positive, the destination is
located in the direction in which the distance decreases, and
therefore, .theta.2(Xa), .theta.2 (Xb) and .theta.2 (Xc) in the
direction in which the distance from the previous location X1
decreases may be used. On the other hand, if .DELTA..phi. is
negative, the destination is located in the direction in which the
distance increases, and therefore, .theta.2(Xb), .theta.2(Xc) and
.theta.2(Xd) in the direction in which the distance from the
previous location X1 increases may be used.
Embodiment 3
[0146] The location tracking method of the present invention
described above can be used as a method for tracking the location
of any of various moving objects by using an acoustic wave, a radio
wave, a light wave or a laser beam. Hereinafter, an ultrasonic
diagnostic apparatus for evaluating a property of a subject's
tissue (e.g., the elasticity thereof, among other things) by the
location tracking method of the present invention will be
described.
[0147] FIG. 20 is a block diagram showing a preferred embodiment of
an ultrasonic diagnostic apparatus according to the present
invention. As shown in FIG. 20, the ultrasonic diagnostic apparatus
includes a transmitting section 102, a receiving section 103, a
tomographic image processing section 104, a tissue tracking section
105, an image synthesizing section 106, an elasticity calculating
section 108, and memories 120 and 121. The apparatus further
includes a control section 100 for controlling all of these
elements. Although not shown, an input device such as a keyboard, a
track ball, a switch, a button or a key and an output device such
as an LCD monitor are also connected to the control section
100.
[0148] In accordance with the instruction given by the control
section 100, the transmitting section 102 generates a high-voltage
signal that drives the probe 101 at a specified timing. The probe
101 converts the signal that has been generated by the transmitting
section 102 into an ultrasonic wave and sends out the ultrasonic
wave toward a subject, which is the object of measurement, and also
detects an ultrasonic echo that has been reflected by an internal
organ of the subject and converts the echo into an electrical
signal. A number of piezoelectric transducers are arranged in the
probe 101. By changing the piezoelectric transducers to use, the
timing to apply a voltage to the piezoelectric transducers, or the
voltages themselves, the probe 101 controls the scan line position,
angle of deflection and focus of the ultrasonic waves to transmit
and receive.
[0149] The receiving section 103 amplifies the received signal, and
adds appropriate delays to the signals received from the respective
piezoelectric transducers. In this manner, the receiving section
103 detects either only an ultrasonic wave that has been reflected
from a predetermined point (i.e., a focused ultrasonic beam) or
only an ultrasonic wave that has come from a predetermined
direction (or at a predetermined angle of deflection). In the
latter case, the receiving section 103 forms an ultrasonic beam so
to speak.
[0150] The tomographic image processing section 104 includes a
filter, a detector, a logarithmic amplifier and a scanning
converter, and analyzes mainly the amplitude of the received
signal, thereby presenting the internal structure of the subject as
an image.
[0151] The tissue tracking section 105 operates in cooperation with
the transmitting section 102 and the receiving section 103 to track
the motions of multiple measuring points that have been set in the
subject's tissue parallel to the ultrasonic wave transmitting and
receiving direction, which is the acoustic line direction of the
ultrasonic waves. The tissue tracking section 105 includes an ASIC,
an FPGA, a DSP, a CPU, a memory and so on, stores a program for
performing respective processing steps of the location tracking
method of the present invention and reads and executes the program
if necessary.
[0152] The blood pressure manometer 111 measures the blood pressure
of the subject and outputs the blood pressure value thus obtained
to the elasticity calculating section 108. The elasticity
calculating section 108 calculates the magnitude of strain given by
Equation (3) based on the motion of the subject's tissue tracked
and the elasticity given by Equation (4) based on the magnitude of
strain and blood pressure value, respectively, and outputs the
elasticity as either a numerical value or a two-dimensional image.
The image synthesizing section 106 synthesizes together at least
the tomographic image and either the elasticity image or the
elasticity value and then presents a synthetic image on the monitor
107. The memory 121 stores the tracking location information, i.e.,
one of the subject tissue's motion, magnitude of strain and
elasticity, which is read in re-calculating the elasticity value
when the transmission and reception of ultrasonic waves are stopped
(which will be referred to herein as a "freeze state"). The memory
120 stores a tomographic image, which is read synchronously with
the elasticity in the freeze state.
[0153] FIG. 21 illustrates a picture that may be presented on the
monitor 107 and shows an exemplary result of measurement of the
vascular wall's elasticity. In FIG. 21, a two-dimensional
elasticity image 201, representing the distribution of elasticity
at a site on the vascular wall in colors, is superimposed on a
vascular wall's monochrome tomographic image 200 on the monitor.
The two-dimensional elasticity image 201 sets the areas to monitor
so as to include a vascular anterior wall adventitia 220, an
anterior wall media 221, an anterior wall intima 222, a blood
vessel lumen 223, a posterior wall intima 224, a posterior wall
media 225, and a posterior wall adventitia 226.
[0154] In transmitting or receiving the ultrasonic wave (which will
be referred to herein as a "live state"), the monochrome
tomographic image 200 is updated at a rate of 10 frames per second
as in a conventional ultrasonic diagnostic apparatus. Meanwhile,
the elasticity image 201 is updated once every cardiac cycle. In
the freeze state, the subject's motion information or magnitude of
strain or elasticity is read from the memory 121, the elasticity is
re-calculated based on that data and displayed, and a tomographic
image is read from the memory 120 and presented synchronously with
the elasticity at that time.
[0155] The monochrome tomographic image 200 is displayed at
monochromatic gray scales corresponding to the reflection
intensities along with a scale 202 indicating the reflection
intensities. On the other hand, the elasticity image 201 is
displayed in color tones corresponding to the elasticity values
along with a scale 203 indicating the elasticity values. Also
displayed under the monochrome tomographic image 200 is a
biomedical signal waveform 204 such as an electrocardiogram.
[0156] According to the present invention, the location of a
measuring point that has been set in a subject can be tracked
precisely, and therefore, the elasticities of respective portions
of the subject and their distribution can be obtained accurately.
Thus, by using the ultrasonic diagnostic apparatus of the present
invention, the degree of advancement of arterial sclerosis on a
vascular wall and its distribution can be measured or a disease
that has been produced on the arterial vascular wall can be
spotted.
[0157] Since the subject's tissue can be tracked accurately by the
tracking method of the present invention, the values to be measured
eventually are not limited to elasticity and magnitude of strain
but may also include other measuring indices such as viscosity
.mu., intima-media thickness (IMT) for use in inspecting arterial
sclerosis and a local pulse wave velocity (PWV) and the cardiac
contraction and dilation function. All of these indices can also be
measured accurately.
[0158] Furthermore, the location tracking method of the present
invention can be used not just in a medical ultrasonic diagnostic
apparatus but also in various other fields as a method for tracking
the location of any of numerous other objects of measurement.
[0159] The location tracking method of the present invention is
applicable to any type of object tracking device that uses any of
various waves such as a flaw detector, a nondestructive tester, a
fish finder and a sonar that use ultrasonic waves, an aircraft
control radar, a weather observation radar, and a military radar
that use electromagnetic waves, and a chartometer and a
displacement meter that use visible radiation, infrared rays and
ultraviolet laser beams.
INDUSTRIAL APPLICABILITY
[0160] The location tracking method of the present invention can be
used not just in the ultrasonic diagnostic apparatus described
above but also in various other fields to track the location of any
of numerous types of objects of measurement.
* * * * *